JP3433643B2 - Image reading device and scanner - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device and a scanner.

[0002]

2. Description of the Related Art FIG. 1 is a schematic perspective view showing the structure of an image reading section 1 of a scanner or a portable copying machine, particularly a handy scanner which is required to be small and lightweight. The image reading unit 1 obliquely irradiates a document P with a light beam f linearly emitted from a light emitting diode (LED) array 2, and the light beam f reflected by the document P is reflected by a rod lens array 3 into a photodiode (PD). ) An image is formed on the array 4, and the original P is read by the photodiode array 4.

As the image-forming optical system on the light-receiving side, a rod lens array 3 is used for downsizing, and its size is very small with a height H = 8 mm. The distance between P and the photodiode array 4 is also T
c = 15 mm, which is extremely low. Therefore, the height dimension of the image reading unit 1 can be made very small.

However, the LED array 2 on the illumination side
Is difficult to miniaturize, and the rod lens array 3
Must be separated from the original P by a predetermined distance L. Therefore, the dimension of the image reading section 1 in the direction orthogonal to the array arrangement direction becomes long, and it is difficult to make the apparatus compact.

FIG. 2 is a perspective view showing the structure of the image reading section 11 of the handy type two-dimensional bar code reader. In the image reading unit 11, the imaging lens 1
A plurality of LEDs 13 are arranged around 2, and a CCD 14 is arranged above the imaging lens 12.

However, the LEDs around the imaging lens 12
The light beam f is irradiated from 13 to the entire original P, and the light beam f reflected by the original P is passed through the imaging lens 12 to the CCD 14
An image is formed on the upper side, and the original P is read by the CCD 14.

However, even in the image reading section 11 of such a two-dimensional bar code reader, since a large number of LEDs 13 are arranged around the image forming lens 12, the arrangement area becomes large, and the image reading section 11 is large. Was a hindrance to compacting.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the drawbacks of the above conventional examples, and an object of the present invention is to miniaturize an image reading device or a scanner.

[0009]

DISCLOSURE OF THE INVENTION An image reading device of the present invention includes an image reading element, an image forming lens for forming an image of an observation surface on the reading element, a light source, and a space between the image forming lens and the observation surface. And a transparent light guide plate for confining the light from the light source and irradiating the light to the observation surface , wherein the light guide plate is separated from
As the thickness of the light guide plate decreases,
The light from the light source
The angle of incidence on the upper surface and the lower surface is reduced,
If the angle of incidence on the lower surface is less than the critical angle for total internal reflection,
It is characterized in that it serves as illumination light for illuminating the observation surface .

In this image reading apparatus, the light emitted from the light source is guided to the light guide plate, the light is radiated from the light guide plate to the observation surface, and the light reflected on the observation surface is passed through the light guide plate to be combined. The image can be formed on the image reading element by the image lens, and the image on the observation surface can be read by the image reading element.

In this image reading device, the light from the light source is guided to the observation surface by the light guide plate, and since the light guide plate is arranged between the imaging lens and the observation surface, the light guide plate, the imaging lens and the image reading element are connected. The image reading devices can be made compact by arranging them so that they overlap each other.

Further, the light guide plate becomes thinner as it gets away from the light source , and total reflection is repeated on the upper and lower surfaces of the light guide plate.
Each time it returns, the light from the light source goes to the top and bottom of the light guide plate.
The angle of incidence is reduced so that the angle of incidence on the bottom surface of the light guide plate is
Illumination light that illuminates the observation surface when it becomes smaller than the critical angle of reflection
Therefore, it is possible to gradually emit light from the light guide plate to the observation surface and uniformly illuminate the observation surface.

Further, by using the light guide plate in contact with the observation surface, the light guide plate can be provided with a function of pressing the observation surface to flatten it, thereby improving the reading accuracy.

By attaching a glass plate to the surface of the resin light guide plate facing the observation surface, the glass plate can be provided with a function of pressing the observation surface to flatten it. Also, by sticking the glass plate, it is possible to prevent the light guide plate from being damaged.

This image reading device can be used for a scanner used in, for example, a computer or a bar code reader.

[0016]

FIG. 3 is a perspective view showing the configuration of an image reading device 21 according to an embodiment of the present invention. The image reading device 21 includes an illumination unit 22, a rod lens array (imaging lens) 23, and a photodiode array 24.
Consists of. The rod lens array 23 is formed by arranging a plurality of cylindrical rod lenses 25 and embedding the rod lenses 25 in a support block 26 made of a light absorbing material (black resin or the like). 25
Indicates that the refractive index is gradually changed along the radial direction around the axis. The photodiode array 24 is arranged above the rod lens array 23, and a plurality of photodiodes (not shown) are mounted on the substrate so as to face the rod lenses 25.

The illumination section 22 is composed of a light guide plate 27 and a light source 28 such as an LED. The light guide plate 27 is formed of a transparent resin having a high refractive index, such as a polycarbonate resin or a methacrylic resin, in a wedge shape that is thin on the front end side and thick on the base end side. The light source 28 is an LED chip 29 housed in a case 30 made of white resin, and the case 30 is opened only on the front surface so that the light f emitted from the LED chip 29 is emitted forward. This light source 28
Are arranged so that the front opening from which the light f exits faces the base end surface of the light guide plate 27. Further, the light guide plate 27 has an area substantially equal to that of the rod lens array 23,
It is arranged immediately below the rod lens array 23. Here, the lower surface of the light guide plate 27 is focused on each light receiving surface of the photodiode array 24.

Therefore, when the image of the original P is read, the lower surface of the light guide plate 27 is placed on the original P in an overlapping manner. Then, when the light source 28 of the illumination unit 22 is caused to emit light to emit the light beam f, the light beam f emitted from the light source 28 enters the inside of the light guide plate 27 from the base end face of the light guide plate 27 as shown in FIG. Incident. The light beam f entering the inside of the light guide plate 27 is
The light guide plate 27 is guided to the tip side while repeating total reflection on the upper surface and the lower surface. Each time the light beam f is repeatedly reflected on the upper surface and the lower surface of the light guide plate 27, the incident angle on the upper surface and the lower surface of the light guide plate 27 becomes gradually smaller. When it becomes smaller than the critical angle of the total reflection at the interface with and, the light beam f is emitted from the upper surface or the lower surface of the light guide plate 27 at an angle close to horizontal. At this time, the light beam f emitted from the lower surface of the light guide plate 27 is
Although it becomes the illumination light for illuminating the document P, the light emitted from the upper surface becomes stray light.

When the light beam f is emitted from the entire lower surface of the light guide plate 27 in this way, the light beam f emitted from the lower surface of the light guide plate 27 illuminates the document P under the light guide plate 27.
The light beam f reflected by the document P passes through the light guide plate 27 from the lower surface to the upper surface, enters the rod lens 25 of the rod lens array 23, and is imaged on the photodiode array 24 by the rod lens array 23. Then, the image of the document P is read by the photodiode array 24.

On the other hand, the light beam f emitted from the upper surface of the light guide plate 27 becomes stray light, but as shown in FIG.
No. 5 does not form the light beam f having a large incident angle and absorbs it inside the rod lens array 23 (support block 26), so that it does not become stray light.

Unlike the light guide plate 27 used for the backlight of the liquid crystal display device, the light guide plate 27 does not have a diffusion pattern or a reflection sheet on the lower surface, and the inclination angle (wedge angle). Since the light beam f reflected by the original P passes through the light guide plate 27 from the lower surface to the upper surface, it does not affect the image formation.

According to such an image reading device 21,
Since the illumination unit 22 can be incorporated under the rod lens array 23, the device can be made compact.

FIG. 6 is a view showing another form of the light guide plate 27 used in the image reading apparatus according to another embodiment of the present invention. In this embodiment, a thin glass plate (cover glass) 31 is adhered to the lower surface of the resin light guide plate 27 using a transparent resin 32. Then, the lower surface of the glass plate 31 is focused on the light receiving surface of the photodiode array 24.

As described above, the glass plate 3 is formed on the lower surface of the light guide plate 27.
By providing 1, the glass plate 31 can be made to have the function of pressing the original, and the original P can be prevented from floating and the image being blurred. Further, the glass plate 31 can prevent the light guide plate 27 from being scratched due to friction with the document P.

The image reading device can be used in various scanners. For example, what is shown in FIG. 7 is a perspective view of a scanner 33 which is an input device for reading a photograph or an illustration and transmitting image information to a personal computer. Further, what is shown in FIG. 8 is a scanner 34 for reading a barcode in a POS system or the like.
The image reading apparatus of the present invention can be used in these scanners. Although not shown, QR (quick
It can also be used as a scanner (head unit) of a barcode reader for reading a two-dimensional code such as a response code).

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing the structure of a conventional image reading device.

FIG. 2 is a perspective view showing the structure of another conventional image reading apparatus.

FIG. 3 is a perspective view showing a structure of an image reading device according to an embodiment of the present invention.

FIG. 4 is an explanatory view of the operation of the image reading apparatus of the above.

FIG. 5 is an explanatory view of the operation of the image reading apparatus of the above.

FIG. 6 is a perspective view showing the structure of an image reading apparatus according to another embodiment of the present invention.

FIG. 7 is a diagram showing a scanner for sending image information to a personal computer.

FIG. 8 is a perspective view showing a scanner for reading a barcode.

[Explanation of symbols]

23 Rod lens array 24 Photodiode array 25 rod lens 27 Light guide plate 28 light source 31 glass plate

Continuation of the front page (56) Reference JP-A-5-308474 (JP, A) JP-A-7-288654 (JP, A) Actual opening 6-62669 (JP, U) Actual opening 2-58229 (JP , U) Showa 58-71261 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 1/04 101

Claims (4)

(57) [Claims] 1. An image reading element, an imaging lens for forming an image of an observation surface on the reading element, a light source, and a light source, and the light is confined between the imaging lens and the observation surface. Bei a transparent light guide plate to irradiate the observation surface Te
The light guide plate becomes thinner as the distance from the light source increases.
The total reflection is repeated on the upper and lower surfaces of the light guide plate.
Light from the light source to the upper surface and the lower surface each time
The incident angle is small, and the incident angle on the lower surface is total reflection.
Illumination that illuminates the observation surface when the angle becomes smaller than the critical angle of
An image reading device that features light . 2. The image reading device according to claim 1, wherein the light guide plate is in contact with the observation surface. 3. The image reading apparatus according to claim 1, wherein the light guide plate is made of resin, and a glass plate is attached to a surface of the light guide plate facing the observation surface. 4. A scanner with a built-in image reading apparatus according to claims 1-3.